Preparation of ascorbic acid and 1-gulosone



Patented May 4, 1943 PREPARATION OF ASCORBIC ACID AND i-GULOSONE Charles G. King and Elam G. White, Pittsburgh, Pa., assignors o1 one-halt to Parke, Davis &- Company, Detroit, Mich, a corporation of Michigan, and one-halt to Abbott Laboratories, North Chicago, Ill., a corporation of Illinois No Drawing. Application October 21, 1935, Serial No. 46,048

' 11 Claims. (01.260-209) The invention relates to a method for synthetically preparing vitamin C.

In the copending application of Charles G. King and William A. Waugh, Serial No. 690,027, flied Sept. 18, 1933, now Patent No. 2,233,417,

to such intermediate compounds themselves as new compositions of matter.

Alpha-keto-l-gulonic acid has the followin formula:

issued March 4, 1941, it was shown that isolated vitamin C could be obtained from certain natural =0 sources such as lemon Juice. It was also shown H-C-OH that isolated vitamin C is a hexuronic acid.

It is now known that vitamin C has the following structural formula: H

Co mon H0 Alpha-keto-l-gulonic acid o Theoretically, alpha-keto-l-gulonic acid can exist in the enolic form having formula: coon HaOH OH 'OH l=ascorblc acid (vitamin C) and is designated as laevo ascorbic acid.

In accordance with our invention, we have been able to prepare l-ascorbic acid (vitamin C) synthetically from certain chemical compounds 2 Enolicform p t -s acid which in themselves have no vitamin C activity. We m'ay start, for example, with d-glucose, a known compound, and by a series of steps hereinafter more fully referred to obtain l-ascorbic In this form it may be considered also to be the enolic form of beta-keto-l-gulonic acid. Betaketo-i-gulonic acid has the following formula:

acid. 39 000E In general our method of synthesis comprises 11- -on the following steps: =0

(1) Reduction of d-glucose to obtain soribitol; I

(2) Oxidation of sorbitol to l-sorbose;

(3) Conversion of l-sorbose into phenyl osa- H- -on zone of sorbose (identical with l-gulosazone); men

(4) Conversion of phenyl gulosazone into Beta-keto-i-gulonic acid l-gulosone;

(5) Oxidation of gulosone to l-aipha-ketoguionic acid;

(6) Conversion of l-alpha-ketogulonic acid to l-ascorbic acid (vitamin C).

Some of the steps in the synthetic preparation as given above were known prior to our invention Prior to the method of synthesizing vitamin C as outlined above it was thought that 'a synthetic preparation could only be prepared-by lactonization of beta-keto-l-gulonic acid to give the gamma-lactone of the following formula:

and it therefore falls within the purview of the present invention to use as a starting material H-(J-OH tor the synthesis such of the intermediate com- =0 pounds above referred to as were known prior to (1) our invention. Thus instead of starting with d-glucose the synthesis may begin with sorbitol, so 11-11-011 l-sorbose or phenyl osazone oi sorbose (l-gulosa- HOH zone).

Our invention relates not only to the method for synthesizing vitamin C but also to the preparation of certain intermediate compounds and Gamma lactoue of beta-keto-l-gulonic acid The above gamma-lactone can also exist in its corresponding enolic form which is identical with l-ascorbic acid (see formula given previously).

.One of the objects of our invention is to provide a synthetic method which can utilize easily available and relatively inexpensive starting materials and which is adaptable to give satisfactory yields.

Other objects of the invention will be more readily apparent after considering. the description hereinafter given.

As stated above, phenyl l-gulosazone can be obtained by methods which have previously been described in the literature. Therefore, the synthesis of vitamin C will be described more in detail as to those steps subsequent to the preparation of this compound. A brief description will be given, however, of the first steps of the process. If d-glucose is the starting material, it may be reduced by methods known in the art to obtain sorbitol. The next intermediate, l-sorbose, may be prepared from sorbitol as follows:

Five hundred grams of compressed bakers yeast is boiled with stirring for hour, centrifuged, and the supernatant liquid diluted with an equal amount of water. Sorbitol is added to the above liquid to give a -10% solution and 500 cc. aliquot portions of this solution are sterilized in l-liter Erlenmeyer flasks. After cooling, 2.5 cc. of glacial acetic acid are added and the liquid inocculated with acetobacter xylinum. After the reducing. sugar content reaches a maximum (usually six to nine weeks) the solution is filtered and pressed out from the thick bacterial films (cellulose), clarified and concentrated. The l-sorbose is present in the solution.

The l-sorbose may then be converted into phenyl l-gulosazone by the following method:

Sixty cc. of phenyl hydrazine and 32 cc. of glacial acetic acid are added to 32 g. of l-sorbose in concentrated aqueous solution. The mixture is stirred for two hours at 70 C., allowed to stand overnight, filtered, washed with dilute acetic acid and water and dried. Yields of 70 to 75 percent of phenyl l-gulosazone are easily obtained by this method.

Synthesis of vitamin C from phenyl l-gulosazone Phenyl l-gulosazone prepared in accordance with the methods given above or obtained from any other source may be used for the synthesis of vitamin C and the following is a specific example of a method which may be used in accordance with our invention.

Twenty grams of phenyl l-gulosazone are dissolved in a solution of 220 cc. of ethanol, 920 cc. H20 and 20 cc. glacial acetic acid at 90 to 95 in a '2-liter, 3-necked flask equipped with a reflux condenser and a mercury seal. Thirty-two grams of benzaldehyde are then added and the mixture stirred vigorously for 1% hours in an atmosphere of nitrogen at 90 to 95. The reaction mixture is then cooled, filtered, extracted five times with ether, and concentrated. A syrup remains containing approximately 2 g. of l-gulosone. This syrupy l-gulosone may be used for the next step in the synthesis comprising oxidation to alphaketo-l-gulonic acid, or, if desired, the syrup may be extracted with absolute alcohol and the alcoholic solution evaporated to dryness in a high vacuum to give a white mass of the solid l-gulosone.

To an aqueous solution of 5 g. of l-gulosone, 1.4 cc. of bromine is added slowly with stirring, after which the solution is allowed to stand at room temperature for two days. The excess bromine is removed by bubbling nitrogen gas through the solution. The hydrobromic acid is removed by leave behind a syrupy mass of the resulting alphaketo-l-Bulonic acid.

The syrupy alpha-keto-l-gulonic acid thus obtained probably contains some synthetic vitamin C (lactone form of the acid) with which it is in equilibrium.

The syrupy material from thebromine oxidation is treated with 20 cc. of 0.2 N HCl and allowed to stand four days at room temperature. The solution is then evaporated to a syrup under diminished pressure in a CO: atmosphere at 50 C. and extracted with acetone. (If there is a residue at this point, the acetone solution may be filtered from it, the residue treated for two hours longer with 20 cc. of 0.2 N HCl at to C. in a C02 atmosphere, the solution evaporated to a syrup and extracted with acetone, and filtered, if necessary to separate from any residue.) The two acetone solutions are combined. Titration of a sample of the combined acetone solutions with 2,6-dichlorophenolindophenol shows that approximateiy 0.6 g. of vitamin C is obtained at this point. The combined acetone solutions are then evaporated to dryness in a C02 atmosphere at 50 C. The residue remaining has a protective action against scurvy, as is shown by animal assay using 1 mg. per day, after previous depletion of guinea pigs on a scorbutic diet. This anti-scorbutic activity has a value corresponding to the titration value obtained with 2,6-dichlorophenolindophenol.

This residue after evaporating on the acetone is a syrupy product and may be used in this form for its antiscorbutic activity or it may be further purified to obtain a crystalline product. The syrupy residue is taken up in a small volume of alcohol and a larger quantity of absolute ether added to precipitate out any impurity. which can be filtered off. The filtrate is then taken down to dryness in a vacuum and the residue trituratcd with a little benzene or petroleum ether or a mixture of equal parts of absolute alcohol and petroleum ether and the triturated mixture allowed to stand at low temperature with occasional stirring to induce crystallization. An alternate process involves conversion into the insoluble lead salt, recovery of the vitamin, and then crystallization from organic solvents as above indicated. In this manner a product melting at 182 to 184 C. is obtained which agrees in this and other properties with the vitamin isolated from natural sources.

Other purification processes may be used, such for example as set forth in the final purification of vitamin C from natural sources, as set forth in Patent No. 2,233,417 previously referred to,

The process of our invention may, of course, be carried out with various modifications not specifically disclosed in the above examples of the steps of the process. For example, instead of using benzaldehyde in preparing the l-gulosone from the gulosazone, substituted benzaldehydes such as bromo or nitro-benzaldehyde may be used. Moreover, in rearranging the alpha-keto- 'l-gulonic acid to the l-ascorbic acid, controlled autoclaving may be used.

Other reagents and other variations in the details which will be obvious to any worker skilled in this art may be used for ca ryin out our new synthesis oi. vitamin C which may be essentially alpha-keto-l-gulonic acid (e. g. using halogen), H101, etc.

acid treatment to gamma lactone form of alpha-keto-l-gulonic acid iorm lactone l-ascorbic acid (vitamin C) out to can] form The last two steps occur practically simultaneously.

. What we claim as our invention is:

1. The process for synthesizing vitamin C comprising the oxidation of l-gulosone to obtain alpha-keto-l-gulon'ic acid and converting the same into l-ascorbic acid.

2. The process for synthesizing vitamin C from sorbitol comprising converting sorbitol by termentation into l-sorbose, treating l-sorbose with 'phenyl hydrazine to obtain phenyl-l-gulosazone, fiydrolizing to obtain l-guloson, oxidizing to, obtain alpha-keto-l-gulonic acid and converting said acid into l-ascorbic acid.

3. In the process of synthesizing vitamin C, the step comprising the treatment or l-gulosone with an oxidizing agent capable oi. converting its -terminal aldehyde group to a carboxy group to moving excess bromine with nitrogen, removing hydrobromic acid with basic lead carbonate, re-

moving excess lead carbonate with hydrogen sulsirup containing alpha-keto-l-gulonic acid.

5. The process for synthesizing vitamin C comprising treating a solution oi alpha-keto-l-gulonic acid with dilute mineral acid, evaporating under diminished pressure in a. non-oxidizing atmosphere to obtain a syrup, extracting the syrup with acetone, removing the acetone, dissolving the residue in alcohol, precipitating impurities with ether, removing alcohol and ether, taking up the residue in ether and crystallizing l-ascorbic acid from the other at low temperature.

6. In the process for obtaining a compound having antiscorbutic properties, the step comprising the treatment oi l-gulosone with an oxidizing agent capable of converting its terminal aldehyde group to a carboxyl group.

I. In the process of synthesizing vitamin C.:

the step comprising the treatment of l-gulosone with an oxidizing agent'oi the class consisting oi. halogen and hydrogen peroxide.

8. In the process for obtaining a compound having antiscorbutic properties, the step comprising the treatment oi. l-guiosone with bromine to convert the terminal aldehyde group to a carboxyl group.

9. In the process for. obtaining a compound having antiscorbutic properties. the step comprising the treatment or l-gulosone with hydrogen peroxide to convert the terminal aldehyde group to a carboxyl group.

10. The process for synthesizing vitamin C comprising treatment of l-gulosone with an oxidizing agent capable of converting its terminal aldehyde group to a car-bowl group, treating the product thus obtained to form a lactone which upon rearrangement to the enol form is l-ascorbic acid.

11. l-Gulosone.

CHARLES G. KING. ELAM G. WHITE. 

